UC Santa Cruz

Remote Direct Memory Access (RDMA) offers high performance through OS kernel bypass and has become a key technology in modern data centers. By exploiting memory-semantic operations, RDMA-based data structures can achieve high scalability and significantly reduce CPU utilization compared with traditional Ethernet-based systems. However, classic sorted indexes such as Skiplist suffer from low throughput under RDMA memory semantics due to frequent and costly remote accesses. To achieve both scalability and high throughput for a lock-based concurrent Skiplist, this paper introduces a hybrid paradigm that combines one-sided and two-sided RDMA operations. This proposal is built upon a re-evaluation of core design choices in RDMA, including transport modes, caching strategies, and memory management. Building on this paradigm, we design HybridSkipList+, a distributed Skiplist system that integrates a client-side coherent cache with pull-based synchronization to reduce expensive network round trips, and a semi-continuous memory allocator to enhance RDMA access locality. We implement HybridSkipList+ on an eight-machine RDMA cluster and conduct extensive evaluations. Results show that HybridSkipList+ outperforms two baseline systems by up to 4.41${\boldsymbol{\times}}$× and 3.45${\boldsymbol{\times}}$× under typical workload conditions.